NEW YORK (Reuters Health) - People who believe a cold remedy will work may indeed feel better sooner -- even if they don't get the real treatment, a new study suggests.

Researchers say their findings are evidence that the so-called placebo effect is at work in recovery from the common cold.

So if the go-to treatment you believe in -- from chicken soup to vitamin C -- is unlikely to do any harm, you might as well stick with it, they say.

The placebo effect refers to a phenomenon seen in clinical trials when people given inactive, fake "treatments" -- like a sugar pill or saline -- show improvements. The placebo effect has been observed in a range of conditions, including chronic pain, depression, inflammatory disorders and even cancer.

For the new study, reported in the Annals of Family Medicine, researchers focused on the common cold -- which famously has no cure.

They randomly assigned 719 people with the beginnings of cold symptoms to one of four groups.

In one group, people were given the herbal cold remedy Echinacea and knew they were taking it. Two other groups were given either Echinacea or a placebo, but participants did not know which they were taking. The fourth group received no pills of any kind.

Overall, there were no significant differences among the groups when it came to the severity or duration of the participants' symptoms -- which lasted about a week in all cases.

But then the researchers focused on the 120 people who, upon entering the study, gave high ratings to Echinacea's effectiveness.

In that group of Echinacea believers, those who were given pills -- Echinacea or placebo -- felt better faster. Placebo users recovered a full 2.5 days sooner than their no-pill counterparts, while Echinacea users were cold-free about 1.5 days sooner.

"That's actually a huge difference," said lead researcher Dr. Bruce Barrett, of the University of Wisconsin, Madison.

"No treatment out there has ever been shown to reduce the duration of colds," Barrett noted in an interview.

He said that the findings offer more evidence that "what people believe about their medicines matters."

As for Echinacea itself, studies have come to conflicting findings about whether the popular herb does in fact work. In an earlier analysis of this same study group, Barrett's team found that (as in this analysis) Echinacea users in general fared no better than the placebo or no-pill groups.

But there was also no evidence that the Echinacea group suffered side effects, like headache, stomach upset or diarrhea, at a higher rate.

And if you have used Echinacea and believe it eases your cold misery, it would "seem reasonable" to continue, according to Barrett.

There are other ways to treat cold symptoms, like acetaminophen for the headache and decongestants for the stuffy nose. But again, those tactics have not been shown to actually cut colds short.

Barrett said he would like to see more people take the simple measures that can make a cold less draining: getting enough rest, taking plenty of fluids to stay hydrated and eating well -- which can include chicken soup.